This invention relates to an electrolytic capacitor having a highly strained elastomeric sealing element, and more particularly to such a capacitor having a wet electrolyte and a package sealing structure wherein the elastomeric element is compressed between an inner plastic sealing member and a glass-to-metal outer seal.
Electrolytic capacitor assemblies employing an outer glass-to-metal seal generally include a solder bead that joins the metal periphery of the glass-to-metal seal to the open end of the capacitor can. The anode wire of the capacitor usually exits the package through a metal tubular eyelet that is central to the outer seal. A specialized need has recently been made known in the industry for a wet electrolyte capacitor that can withstand 200 cycles of temperature cycling from -55.degree. C. to 125.degree. C. after which there should be no evidence of electrolyte attack and corrosion of the solder bead and no higher d.c. leakage current than 200% of the initial rated d.c. leakage limit. No more than one failure would be allowed in each group of 32 capacitors tested. During severe temperature cycling, the repetitive relative movement of the sealing elements due to differential thermal coefficients of expansion tend to rupture the seals that had been formed between the sealing elements. In particular, the most prevalent rupturing of the seal tends to occur between the anode riser wire and the inner sealing member or members, admitting liquid electrolyte to the glass surface that insulates the anode from the can or cathode. This results in a d.c. leakage current path shunting the capacitor and further admits the liquid electrolyte to the solder bead region where corrosion and eventually electrolyte leakage may occur. Also, the smaller the diameter of the capacitor becomes, the more difficult it is to make a capacitor seal that is capable of meeting this thermal cycling test.
It is a primary object of this invention to provide a wet electrolyte capacitor that is capable of meeting the above noted severe temperature cycling test.
It is a more narrow object of this invention to provide a sealing structure for a wet electrolyte capacitor that is especially suitable for use in small diameter capacitors, e.g. less than 0.220 inch (0.559 cm).